Re: [PATCH] KVM: PPC: Book3S HV: Fix IRQ map warnings with XICS on pSeries KVM Guest

[Vaibhav Jain <vaibhav@linux.ibm.com>]

Thanks Amit for the patch.

Amit Machhiwal <amachhiw@linux.ibm.com> writes:
> The commit 9576730d0e6e ("KVM: PPC: select IRQ_BYPASS_MANAGER") enabled
> IRQ_BYPASS_MANAGER when CONFIG_KVM was set. Subsequently, commit
> c57875f5f9be ("KVM: PPC: Book3S HV: Enable IRQ bypass") enabled IRQ
> bypass and added the necessary callbacks to create/remove the mappings
> between host real IRQ and the guest GSI.
>
> The availability of IRQ bypass is determined by the arch-specific
> function kvm_arch_has_irq_bypass(), which invokes
> kvmppc_irq_bypass_add_producer_hv(). This function, in turn, calls
> kvmppc_set_passthru_irq_hv() to create a mapping in the passthrough IRQ
> map, associating a host IRQ to a guest GSI.
>
> However, when a pSeries KVM guest (L2) is booted within an LPAR (L1)
> with the kernel boot parameter `xive=off`, it defaults to using emulated
> XICS controller. As an attempt to establish host IRQ to guest GSI
> mappings via kvmppc_set_passthru_irq() on a PCI device hotplug
> (passhthrough) operation fail, returning -ENOENT. This failure occurs
> because only interrupts with EOI operations handled through OPAL calls
> (verified via is_pnv_opal_msi()) are currently supported.
>
> These mapping failures lead to below repeated warnings in the L1 host:
>
>  [  509.220349] kvmppc_set_passthru_irq_hv: Could not assign IRQ map for (58,4970)
>  [  509.220368] kvmppc_set_passthru_irq (irq 58, gsi 4970) fails: -2
>  [  509.220376] vfio-pci 0015:01:00.0: irq bypass producer (token 0000000090bc635b) registration fails: -2
>  ...
>  [  509.291781] vfio-pci 0015:01:00.0: irq bypass producer (token 000000003822eed8) registration fails: -2
>
> Fix this by restricting IRQ bypass enablement on pSeries systems by
> making the IRQ bypass callbacks unavailable when running on pSeries
> platform.
>
> Signed-off-by: Amit Machhiwal <amachhiw@linux.ibm.com>

Reviewed-by: Vaibhav Jain <vaibhav@linux.ibm.com>

> ---
>  arch/powerpc/kvm/book3s_hv.c | 20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 19f4d298dd17..7667563fb9ff 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -6541,10 +6541,6 @@ static struct kvmppc_ops kvm_ops_hv = {
>  	.fast_vcpu_kick = kvmppc_fast_vcpu_kick_hv,
>  	.arch_vm_ioctl  = kvm_arch_vm_ioctl_hv,
>  	.hcall_implemented = kvmppc_hcall_impl_hv,
> -#ifdef CONFIG_KVM_XICS
> -	.irq_bypass_add_producer = kvmppc_irq_bypass_add_producer_hv,
> -	.irq_bypass_del_producer = kvmppc_irq_bypass_del_producer_hv,
> -#endif
>  	.configure_mmu = kvmhv_configure_mmu,
>  	.get_rmmu_info = kvmhv_get_rmmu_info,
>  	.set_smt_mode = kvmhv_set_smt_mode,
> @@ -6662,6 +6658,22 @@ static int kvmppc_book3s_init_hv(void)
>  		return r;
>  	}
>  
> +#if defined(CONFIG_KVM_XICS)
> +	/*
> +	 * IRQ bypass is supported only for interrupts whose EOI operations are
> +	 * handled via OPAL calls. Therefore, register IRQ bypass handlers
> +	 * exclusively for PowerNV KVM when booted with 'xive=off', indicating
> +	 * the use of the emulated XICS interrupt controller.
> +	 */
> +	if (!kvmhv_on_pseries()) {
> +		pr_info("KVM-HV: Enabling IRQ bypass\n");
> +		kvm_ops_hv.irq_bypass_add_producer =
> +			kvmppc_irq_bypass_add_producer_hv;
> +		kvm_ops_hv.irq_bypass_del_producer =
> +			kvmppc_irq_bypass_del_producer_hv;
> +	}
> +#endif
> +
>  	kvm_ops_hv.owner = THIS_MODULE;
>  	kvmppc_hv_ops = &kvm_ops_hv;
>  
>
> base-commit: 6e3597f12dce7d5041e604fec3602493e38c330a
> -- 
> 2.49.0
>

-- 
Cheers
~ Vaibhav